From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from homiemail-a96.g.dreamhost.com (caiajhbdcahe.dreamhost.com [208.97.132.74]) by huchra.bufferbloat.net (Postfix) with ESMTP id 1063421F13F for ; Thu, 28 Mar 2013 09:10:05 -0700 (PDT) Received: from homiemail-a96.g.dreamhost.com (localhost [127.0.0.1]) by homiemail-a96.g.dreamhost.com (Postfix) with ESMTP id 53D7B3B8062; Thu, 28 Mar 2013 09:10:04 -0700 (PDT) Received: from kmn.local (c-24-4-217-203.hsd1.ca.comcast.net [24.4.217.203]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: nichols@pollere.net) by homiemail-a96.g.dreamhost.com (Postfix) with ESMTPSA id 2384B3B805B; Thu, 28 Mar 2013 09:10:04 -0700 (PDT) Message-ID: <51546B6A.5020207@pollere.com> Date: Thu, 28 Mar 2013 09:10:18 -0700 From: Kathleen Nichols User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: codel@lists.bufferbloat.net References: <515381EB.8030709@superduper.net> In-Reply-To: <515381EB.8030709@superduper.net> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Codel] sawtooth X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Mar 2013 16:10:05 -0000 For a single TCP using reno and with an RTT at the nominal 100ms level, you can expect to see about 75% utilization of the link. If you use cubic, you do better. If you tolerate more queue, you get more utilization but more delay. Van talked about how we pick the set points at the IETF, http://www.ietf.org/proceedings/84/slides/slides-84-tsvarea-4.pdf For more on this, you can see our old Red in a Different Light draft, page 6, http://www.cnaf.infn.it/~ferrari/papers/ispn/red_light_9_30.pdf It's important to figure out what your objective is and measure that. There is the link utilization for a single TCP flow, the goodput of a particular flow, the delay experienced. Then there is peformance of more than one flow. Kathie On 3/27/13 4:34 PM, Simon Barber wrote: > I've been thinking about codel's behaviour with a single TCP stream. TCP > in steady state exhibits a sawtooth cwin behaviour. cwind rises by 1 > each RTT until the queue drops a packet, then cwind halves, and repeat. > > With codel the earliest a packet will be dropped is 100ms after the > queue size grows to the point the sojourn is 5ms. At this point the cwin > is halved. For small RTTs or with multiple flows this may ensure good > utilisation, but for large RTTs and a single flow surely dropping this > early could result in starvation? > > Simon > _______________________________________________ > Codel mailing list > Codel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/codel